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24/07/2024 14:47:36

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printТренировка 3

printA. Average distance

Ограничения: время – 3s/6s, память – 64MiB Ввод: input.txt или стандартный ввод Вывод: output.txt или стандартный вывод copy
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Given a tree, calculate the average distance between two vertices in the tree. For example, the average distance between two vertices in the following tree is `(d_01\ +\ d_02\ +\ d_03\ +d_04\ +\ d_12\ +\ d_13\ +\ d_14\ +\ d_23\ +\ d_24\ +\ d_34)/10\ =\ (6+3+7+9+9+13+15+10+12+2)/10\ =\ 8.6`.
4094.jpg
Figure 1: The first sample case
Input
On the first line an integer `t` `(1\ ≤\ t\ ≤\ 100)`: the number of test cases. Then for each test case:
One line with an integer `n` `(2\ ≤\ n\ ≤\ 10000)`: the number of nodes in the tree. The nodes are numbered from 0 to n 1.
`n-1` lines, each with three integers `a` `(0\ ≤\ a\ <\ n)`, `b` `(0\ ≤\ b\ <\ n)` and `d` `(1\ ≤\ d\ ≤\ 1000)`. There is an edge between the nodes with numbers `a` and `b` of length `d`. The resulting graph will be a tree.
Output
For each testcase:
One line with the average distance between two vertices. This value should have an absolute error of at most `10^{-3}`.

Sample Input

1
5
0 1 6
0 2 3
0 3 7
3 4 2

Sample Output

8.600
Source: Benelux Algorithm Programming Contest 2007
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